Jeffery Durbin and Dimitris Stergiedis, UMass students, will present their first year project reports.
Presenter: Jeffery Durbin
Tile: Characterizing the Visuospatial Sketchpad: Rehearsal and Retrieval in Visual Short-Term Memory
Abstract: Sternberg’s (1966) classic short-term memory task produces apattern of reaction times (RTs) suggestive of serial exhaustive search through memory when subjects are given ample time to encode the memory set items and establish a rehearsal sequence. However, if the memory set items are presented quickly, RTs and accuracy reveal a parallel search process with a strong recency gradient (i.e., recently studied items are recognized more quickly and accurately).
These phenomena have been well described for verbal material, but few studies have addressed the dynamics of rehearsal and search for purely visuospatial information and no studies have examined RTs following slow sequential presentation of the memory set. To address whether sequential rehearsal occurs for visuospatial information, we developed a novel visuospatial short-term memory task in which participants saw a sequence of colored dots (500 ms per dot) along a horizontal line and, after a brief delay (500 ms mask), gave a binary “old” / “new” response to a single test item. We compared four versions of the task, which varied in how similar the lures were to the items in the study sequence: lures were either a recombination of a previously viewed color and location (both old), a new color in an old location (new color), an old color in a new location (new location), or a new color in a new location (both new). Neither RTs nor accuracy revealed a pattern indicative of serial search in any of these conditions, suggesting a lack of sequential rehearsal. A recency gradient was observed for conditions in which color information was necessary (new color, both old), with negligible set size effects across the gradient. In contrast, the recency gradient was reduced for conditions where location information could serve as the sole dimension of evaluation (new location, both new), and set size effects were seen at each level of recency. These findings suggest that color information suffers from strong retroactive interference such that previous color representations are “overwritten,” whereas location representations are blurred with each presentation, as if the location information has been “averaged.”